1. Field of the Invention
The invention is generally related to biological detection.
2. Description of Related Art
With the notable exception of glucose sensors, the vast majority of rapid detection/measurement systems use antibodies for recognition, identification, and quantification of biological targets. Antibody-based detection techniques are powerful, versatile tools for various molecular and cellular analyses, environmental monitoring, and clinical diagnostics. This power originates from the specificity of the antibodies for their particular antigenic sites.
Antibody-based recognition of targets is the basis for detection in many optical and electrochemical biosensors (e.g., interferometers, reflectometric interference spectoscopic sensors, resonance minor sensors, surface plasmon resonance instruments, quartz crystal microbalances, light-addressable potentiometric sensors, electrochemiluminescence systems, fiber optic, and array biosensors), as well as in flow cytometry and non-sensor detection techniques such as lateral flow assays.
Detection techniques employing antibodies, although considered less sensitive than polymerase chain reaction-based systems, are still highly sensitive, are well characterized, and have been adapted for use in rapid assay systems. Due to the specificity of the antibodies, many of these immunoassay-based systems have the additional benefit of requiring little if any sample preparation prior to analysis.
However, assays utilizing antibodies for specific recognition of target analytes have a number of problems that may significantly limit their widespread use in the field: 1) many antibodies are sensitive to environmental temperatures and must be stored frozen, refrigerated, or lyophilized for retention of optimal activity; 2) at least one antibody or set of antibodies is required for each target of interest in multiplexed assays, increasing the complexity and potential for non-specific or cross-reactive binding; 3) specificity and sensitivity of antibody-based recognition may, in some cases, be mutually exclusive; 4) target-specific antibodies may not be available due to the non-antigenic nature of the analyte; and 5) although monoclonal antibodies are, by their very nature, more consistent than polyclonal antibodies, development and large-scale production of monoclonals is expensive and time-consuming.
The biological detection and clinical diagnostic markets are currently dominated by antibody-based assays. However, antibody-based assays may never be stable enough for long-term sensor applications; such stability is critical for fielding sentry-type systems and for non-laboratory use. Use of antimicrobial peptides and antibiotics should improve the current logistical burdens required of fielded systems.
Many organisms, including mammals, insects, amphibians, fish, crustaceans, plants and bacteria, produce antibiotics and antimicrobial peptides as part of their innate immune systems for protection against invasion by harmful microbes. Antimicrobial peptides and some antibiotics recognize target pathogens by interacting with the microbial cell membranes. Most peptide-membrane and antibiotic-membrane interactions do not involve specific receptors, but rather invariant components of the cell surface; binding is therefore semi-selective—each peptide or antibiotic can bind to multiple microbial species with differing affinities. As natural evolution has conferred upon many of these compounds the stability to withstand adverse conditions (polluted ponds, etc.) and the ability to recognize multiple microbial species, assays using these peptides and antibiotics for recognition should have the following advantages over conventional antibody-based screening methods: stability, resistance to proteases, ability to detect larger numbers of species than a corresponding number of antibodies, and a lower degree of complexity for multi-analyte screening assays.